Analog Circuits and Systems

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1 Analog Circuits and Systems Prof. K Radhakrishna Rao Lecture 3 Role of Analog Signal Processing in Electronic Products Part 11 1

2 Cell Phone o The most dominant product of present day world o Its basic function is to make and receive telephone calls over a radio link while moving around a wide geographic area. o It connects to a cellular network provided by a mobile phone operator, allowing access to the public telephone network. o They also support a wide variety of other services such as text messaging, multimedia messaging, , Internet access, short-range wireless communications (infrared and Bluetooth), business applications, gaming, and photography. o Mobile phones that offer these and more general computing capabilities are referred to as smart phones. 2

3 Cell Phone Block Diagram (Md Whaiduzzaman, Abdulla Gani: A Study of Anatomy of Smartphone; Computer Communication and Collaboration, 2013) 3

4 Radio and Analog Base Band Block Diagram 4

5 RF Front End o Typical path consists of, after diplexer, a tunable band pass filter, RF low transmitting power of cell phone is 500mW o RF filter in the transmission path is a tunable band pass filter o Antenna is connected to transmitter and receiver through a diplexer o Low noise amplifier (LNA) 5

6 IF Block o The output of the LNA goes to a mixer to generate IF signal using the local oscillator that is under the control of digital base band processor to produce a sinusoidal signal at ( IF ). o The IF signal is amplified by IF amplifier which is a fixed frequency band pass filter o The IF amplifier output is demodulated using local oscillator which down converts the signal to analog/digital base band. 6

7 Analog Back-End and Baseband o The output of the demodulator may represent the digitally coded speech, video or data. o The video signal and speech signal are reconstructed using D/A converter. The digital data directly goes to the digital base band processor o The output from IF amplifier whose input is from the Modulator is up converted to the radio frequency of transmission by a mixer and power amplified before getting connected to the antenna. 7

8 Analog Back-End and Baseband (contd..) o Speech and video signals generated by the user are converted into digital data using Analog-to-Digital converter. o Digital data goes to the Modulator and to digital base band processor 8

9 Digital Baseband o Human interface (keyboard and display), dialing, memory and power management are controlled by digital baseband processor 9

10 Power Management o Power management system consists of battery charging, battery monitoring and efficient power distribution o Digitally controlled analog sub-systems. 10

11 Electrocardiogram (ECG) o An electrocardiogram (ECG) is a non-invasive procedure for recording of the electrical activity on the body surface generated by the heart. o An electrocardiogram (ECG or EKG) shows a series of waves that relate to the electrical impulses of heartbeat. 11

12 Idealized version of ECG Waveform o It has features defined as the P, QRS, and T for each heartbeat. o The amplitude and relative timing of the various segments (PQRST) are used for diagnosis. 12

13 Important Components of ECG o Heart rate: Hz (i.e beats per minute) o P-wave: Hz o QRS: Hz o T-wave: 1 7 Hz o High frequency potentials: Hz 13

14 Artifacts and Noise in ECG o Muscle: 5 50 Hz o Respiratory: Hz (e.g bpm) o External electrical: 50 or 60 Hz (A/C mains or line frequency) o Other electrical: typically >10 Hz (muscle stimulators, strong magnetic fields, pacemakers with impedance monitoring) 14

electrodes that occur at each heartbeat and records them on

15 ECG Recording o It uses several electrodes o The machine detects and amplifies the electrical impulses picked up by electrodes that occur at each heartbeat and records them on to a paper, computer or any storage device. (google images) 15

16 Positioning of Electrodes o A differential recording between two points on the body are made o They are defined as V I, V II and V III (google images) where RA = right arm, LA = left arm, and LL = left leg 16

17 ECG Signal Characteristics 17

18 ECG Block Diagram 18

19 Analog Front End The inputs from groups of electrodes are multiplexed and processed for common mode rejection by the instrumentation amplifier (INA) The output of INA is amplified by the variable gain amplifier Frequencies lower than 0.05 Hz are eliminated by High Pass Filter Frequencies above 150 Hz are eliminated by Low Pass Filter The noise at power supply frequency is eliminated using a Notch Filter 19

20 Analog Front End (contd..) o The output of the notch filter is amplified and coded to digital form using an Analog-to-Digital Converter o The digital data is suitable processed by a Digital Signal Processor for recording, display or storage. 20

21 Basic Analog Signal Processing Functions o Amplification/Attenuation o Filtering o Comparison o Multiplication o Digital-to-Analog Conversion o Analog-to-Digital Conversion 21

22 Amplification/Attenuation o Output (voltage or current) = K x Input (voltage or current)+offset; where K >1 or K < 1 = a i x Input i where a i can be positive or negative (addition and/or subtraction o If X1 and X2 are two independent variables (inputs) (X1+X2)/2 is known as common mode signal (X1-X2) is known as differential mode signal o Ideal Difference Amplifier: Output=Kd x (X1-X2) 22

23 Amplification/Attenuation (contd..) o Non-ideal Difference Amplifier: Output = Kd x (X1-X2) + Kc x (X1+X2)/2 where Kd is known Differential Mode Gain and Kc is Common Mode Gain o (Kd/Kc) = is known as Common Mode Rejection Ratio. It is normally expressed in decibels as 20log o An ideal difference amplifier should have Common Mode Rejection Ratio of. 23

24 Filtering o Filtering is rejecting or accepting signals in bands of frequencies o Filtering can be Low Pass, High Pass, Band Pass and Band Stop 24

25 Low Pass Filtering o An ideal low pass filter will pass all frequency components below a specified frequency known as upper cut off frequency o A non-deal low pass filter causes varying amplification/ attenuation of frequency components around the upper cut off frequency 25

26 High Pass Filtering o An ideal high pass filter will pass all frequency components above a specified frequency known as lower cut off frequency o A non-deal high pass filter causes varying amplification/ attenuation of frequency components around the lower cut off frequency 26

27 Band Pass Filtering o An ideal band pass filter will pass all frequency components within a upper cut off frequency and lower cut off frequency o A non-deal high pass filter causes varying amplification/ attenuation of frequency components around the upper and lower cut off frequencies 27

28 Band Stop Filtering o An ideal band stop filter will stop all frequency components y within a upper cut off frequency and lower cut off frequency o A non-deal band stop filter causes varying amplification/ attenuation of frequency x components around the upper and lower cut off frequencies 28

29 Comparison o When the input is less than a reference value the output has a specified fixed value and when the input is more than the reference value the output has another specified fixed value 29

30 Multiplication o The output of a multiplier is the product of two inputs o An ideal multiplier has a relationship V = K V V 0 0 X Y o where V X and V Y are two independent inputs o A non-ideal multiplier will have relationship V = V + K V + K V + K V V 0 offset X X Y Y 0 X Y where K X V X and K Y V Y are feed through components 30

31 Multiplication Applications in Communication KVV ( )( ) o p1 p2 a)v ( ) ( ) o = Ko Vp1sin ω1t Vp2sin ω 2t = cos 1 2 t cos 1 2 t 2 ω ω ω +ω DSB, Balance Modulator and Mixer ( )( ) b)v = K V sin ωt V sin ωt sin ω t = K V o o p1 1 p2 2 1 o p1 DSB Demodulation ( 1 cos 2ω1 t ) V sin ω t p2 2 KVV c)vo = Ko Vp1sin ωt Vp2sin ω t +φ = cos cos 2 t 2 φ ω +φ Phase detector, frequency doubler ( )( ( )) o p1 p2 ( ) 2 31

32 Digital to Analog Conversion o The input is n-bit digital data and the output is analog signal o Output = i= 1, n n a 2 V wherea i ref i o It can also be called a multiplier with V ref as analog input = 1 0 and { aa... } 1 2 an is the digital signal 32

33 Analog to Digital Conversion o The output is n-bit digital data and the input is analog signal o A comparator is a one-bit A/D converter 33

34 Analog Systems require o Signal Generation 2 v + 2 Kv = 0 t p ( ) v = V sin Kt +φ ω= K o Power Supplies 34

6.101 Introductory Analog Electronics Laboratory

6.101 Introductory Analog Electronics Laboratory Spring 2015, Instructor Gim Hom Project Proposal Transmitting, Receiving, and Interpreting ECG Waveforms Daniel Moon (dhmoon@mit.edu) Thipok (Ben) Rak-amnouykit